C4 Differential equation help
http://www.ocr.org.uk/Images/59547-question-paper-unit-4724-01-core-mathematics.pdf
Question 9ii)
For the constant c I get ln140 in the mark scheme it says -ln140 I can't seem to figure out why.
My working out :
1 / ( 160 - theta) d theta = k dt
ln ( 160 - theta) = kt + c
When t = 0 theta = 20
ln140 = 0 + c
Question 9ii)
For the constant c I get ln140 in the mark scheme it says -ln140 I can't seem to figure out why.
My working out :
1 / ( 160 - theta) d theta = k dt
ln ( 160 - theta) = kt + c
When t = 0 theta = 20
ln140 = 0 + c
(edited 11 years ago)
Original post by IShouldBeRevising_
http://www.ocr.org.uk/Images/61388-question-paper-unit-4722-01-core-mathematics-2.pdf
Question 9ii)
For the constant c I get ln140 in the mark scheme it says -ln140 I can't seem to figure out why.
My working out :
1 / ( 160 - theta) d theta = k dt
ln ( 10 - theta) = kt + c
When t = 0 theta = 20
ln140 = 0 + c
Question 9ii)
For the constant c I get ln140 in the mark scheme it says -ln140 I can't seem to figure out why.
My working out :
1 / ( 160 - theta) d theta = k dt
ln ( 10 - theta) = kt + c
When t = 0 theta = 20
ln140 = 0 + c
you missed a minus sign when you integrated the LHS!
Original post by davros
you missed a minus sign when you integrated the LHS!
I don't understand
Original post by IShouldBeRevising_
http://www.ocr.org.uk/Images/59547-question-paper-unit-4724-01-core-mathematics.pdf
Question 9ii)
For the constant c I get ln140 in the mark scheme it says -ln140 I can't seem to figure out why.
My working out :
1 / ( 160 - theta) d theta = k dt
ln ( 160 - theta) = kt + c
When t = 0 theta = 20
ln140 = 0 + c
Question 9ii)
For the constant c I get ln140 in the mark scheme it says -ln140 I can't seem to figure out why.
My working out :
1 / ( 160 - theta) d theta = k dt
ln ( 160 - theta) = kt + c
When t = 0 theta = 20
ln140 = 0 + c
Temperature is increasing so:
(edited 11 years ago)
Original post by joostan
Temperature is decreasing so:
You can say k, but then you must remember that k is a negative constant.
You can say k, but then you must remember that k is a negative constant.
The question says increasing ?
Original post by IShouldBeRevising_
The question says increasing ?
ah, misread the q COMPLETELY!
poor show 
see above.(edited 11 years ago)
Original post by IShouldBeRevising_
The question says increasing ?
Allow me to try again.
what does 160-theta differentiate to?
Original post by joostan
Allow me to try again.
what does 160-theta differentiate to?
what does 160-theta differentiate to?
-1 ?
Original post by IShouldBeRevising_
-1 ?
So as davros says - where is the minus on the LHS?
f'(x)/f(x) = -1/(160-theta)
So the integral should read -[-1/(160-theta)]
Original post by joostan
So as davros says - where is the minus on the LHS?
f'(x)/f(x) = -1/(160-theta)
So the integral should read -[-1/(160-theta)]
f'(x)/f(x) = -1/(160-theta)
So the integral should read -[-1/(160-theta)]
But originally the lhs = 1/160 - thetA
d/dx(1/ 160 - theta ) = -1 however the original lhs is 1 not -1?
Original post by IShouldBeRevising_
But originally the lhs = 1/160 - thetA
d/dx(1/ 160 - theta ) = -1 however the original lhs is 1 not -1?
d/dx(1/ 160 - theta ) = -1 however the original lhs is 1 not -1?
when you integrate 1/(160 - theta) you should get -ln|160 - theta|
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